Stationary Vehicle Battery Charger Modulation Strategy

This invention was made with government support under the DE-EE0009869 contract, awarded by the United States Department of Energy, Energy Efficiency & Renewable Energy EE-1 Office. The U.S. Government has certain rights in the invention.

The present application relates generally to stationary vehicle battery chargers and more particularly to a stationary vehicle battery charger modulation strategy.

This background description is set forth below for the purpose of providing context only. Therefore, any aspects of this background description, to the extent that it does not otherwise qualify as prior art, is neither expressly nor impliedly admitted as prior art against the instant disclosure.

Past stationary vehicle battery chargers include a plurality of power modules and charging plugs that electrically connect the power modules to a battery electric vehicle (BEV). The number of power modules that supply electric current to a BEV can selectively vary and the power modules are not typically synchronized among each other. Thus, as the number of power modules used with one plug increases, the possibility that the current output aligns in-phase and the additive nature of the currents can exceed relatively stringent ripple current thresholds. Stationary vehicle battery chargers can compensate for larger ripple currents using an inductor-capacitor (LC) circuit. But the capacitor and inductor in such a circuit add cost to the vehicle battery charger. It would be helpful to regulate the ripple current without the use of such an LC circuit.

In one implementation, a method is provided of operating a stationary vehicle battery charging system having a first plurality of power modules and a second plurality of charging plugs. The method includes the step of establishing a synchronization block comprising two or more of the first plurality of power modules for charging through one of the charging plugs connected to a battery electric vehicle (BEV). The method further includes the steps of communicating at least one synchronization signal among the synchronization block power modules to synchronize respective outputs for reducing charging ripple and charging the BEV using the synchronization block power modules.

A system for operating a charging system is also presented.

1 FIG. 10 10 12 14 16 10 12 12 10 18 10 14 Referring now to the drawings wherein like reference numerals are used to identify identical or similar components in the various views,is a simplified diagrammatic and block diagram view depicting an implementation of a stationary vehicle battery electrical charging system. The systemis configured to be electrically connected to a source of AC power such as an electrical gridand is further configured generally to output DC power for a DC load, such as a battery electric vehiclefor directly charging a rechargeable batterythereof. The charging systemmay be a DC fast charging system. The gridmay include any one of a number of electrical power generators and electrical delivery mechanisms. In an embodiment, the gridmay provide three-phase AC power at 480 VAC at 60 Hz. As shown, the systemincludes an output connector or charging plugconfigured for use in connecting the output of the systemto the BEV.

10 20 22 24 26 28 28 28 30 32 a b c The systemfurther includes a plurality of power modules, a plurality of dispensers, direct current (DC) delivery cables, a switch matrix, first, second, and third communication buses,,, respectively, and a main controlconnected to the dispensers and power modules via a network facility.

20 1 2 3 4 5 6 7 8 1 8 12 12 24 1 8 10 1 8 1 8 1 FIG. The power modulesare configured to convert AC power into DC power.shows eight individual power modules designated PM, PM, PM, PM, PM, PM, PM, and PMalthough it should be understood that the illustration of eight power modules is for description purposes only. Each module PM-PMis electrically connected, at an input thereof, to the gridand is configured generally to rectify input AC power from the gridand output DC power (when active) to a respective one of the DC delivery cables. Each power module PM-PMtherefore generates an output signal having a DC component. In addition, each output signal from a power module also has an AC component corresponding to a ripple current and voltage. The AC component may have a frequency at the grid line frequency or alternatively at some other frequency that is dependent on the particular conversion topology being used in the power modules of charging system. In an embodiment, each module PM-PMmay be configured to have a DC output power capacity of various magnitudes (e.g., 60 kW). The AC/DC electrical power conversion functionality of the power modules PM-PMmay comprise approaches known in the art.

22 18 14 16 1 2 3 4 5 6 7 1 7 26 1 8 18 18 1 FIG. The dispensersare configured to include a respective charging plugconfigured to be connected to an input port or the like of a battery electric vehicle (BEV)to directly charge the BEV's rechargeable battery.shows seven individual dispensers designated D, D, D, D, D, D, and D, although it should be understood that the illustration of seven dispensers is for description purposes only. Dispensers D-Dare each electrically connected to the switch matrixto access DC power originating from one or more of the power modules PM-PMand each also includes a respective connector (or charging plug). While each dispenser is illustrated as including one charging plug, it should be understood that this is exemplary only and not limiting in nature.

24 1 8 26 24 DC delivery cablesinclude a plurality of individual cables so as to provide respective electrically conductive paths from each power modules PM-PMto the switch matrix. The cablesmay comprise conventional materials and construction.

26 24 1 7 26 1 8 1 7 26 26 26 The switch matrixhas an input side configured to receive DC delivery cablesand an output side connected to the dispensers D-D. The switch matrixis configured to connect any one or more of the power modules PM-PMto a dispenser (one of D-D). While the switch matrixis illustrated as separate switching equipment apart from the power modules and dispensers, it should be understood that this is for purposes of description only. In other embodiments, the switch matrixmay be incorporated into the power module (or power cabinet—not shown), dispenser, both, or as separate switching equipment as shown. The switch matrixmay comprise conventional materials and construction.

28 28 28 28 28 28 28 22 1 8 a b c a c a The communication data buses,, andare configured for intra-power module communications, intra-dispenser communications, and inter-power module-dispenser communications, respectively. It should be understood that while three separate buses-are shown, this is for purposes of description only and alternatively a single busmay be provided to support all of the above-described communications. In an implementation, at least the communication data busis a bidirectional data bus that connects the power modules(PM-PM) for bidirectional communications therebetween.

30 10 1 8 1 7 10 30 1 8 18 14 18 30 10 32 The main controlis configured to provide oversight control of the operation of the charging system, receiving status and operating data from power modules PM-PMand dispensers D-Das well as providing additional functionality to the operation of the system. For example, the main controlcan be configured to assign one or more of the power modules PM-PMto one of the charging plugsfor purposes of servicing the power request made by the BEVinto which the charging plughas been inserted. The main controlis configured to communicate with the other components of the charging systemthrough a network interface and underlying network transport facility, which may comprise conventional communications components.

As described in the Background, an off board charging system often makes use of several power modules concurrently working in the charging process. The operation of the different power modules in the charging system may be coordinated at some level, for example, with respect to a charging start time and charging stop time, the management of faults, as well as implementing a charging profile requested by the battery electric vehicle (BEV). One of the most stringent requirements in the charging standards pertains to electrical current and voltage ripple limits. Because the operation of the power modules is not synchronized in these types of background charging systems, their current and voltage outputs can be in-phase or close to being in phase, such that a ripple current and voltage effect becomes additive. Such charging systems often comply with applicable ripple limits through a hardware approach involving the use of an expensive external filter (e.g., an inductor/capacitor LC filter).

18 According to an implementation, a modulation strategy for controlling a stationary vehicle battery charger involves determining and exchanging a synchronization signal between two or more power modules included in a so-called synchronization block. A synchronization block defines those power modules whose output will be combined (i.e., summed) to supply power to and through a single charging plug(i.e., those power modules assigned to the same plug). Thus, for example, in a two power module synchronization block, a first power module generates a first output signal having a first DC component and a first AC component, and a second power module generates a second output signal having a second DC component and a second AC component. Individually, the first AC component output may have a certain frequency and a certain ripple magnitude. Individually, the second AC component may also have the same general frequency and the same general ripple magnitude.

The operation and resulting outputs of the power modules in any particular synchronization block will be synchronized in accordance with the above-mentioned synchronization signal, which contains information that allows the power modules to selectively phase shift their outputs to reduce a ripple magnitude of the combined AC components (ripple) of the synced power modules.

The modulation strategy described herein differs from charger systems where power module output signals assigned to a particular charging plug are being generated in-phase or close to being in-phase. In contrast, the modulation strategy described herein is configured for phase shifting outputs so that the outputs are not in-phase or close to being in-phase so that the combined ripple current or voltage is reduced to acceptable levels.

2 FIG. 1 8 38 38 40 42 44 40 40 44 42 40 42 40 44 is a block diagram depicting one of the power modules PM-PMin greater detail, designated as a power module. The power moduleincludes an electronic processor, a memory, and an AC/DC power conversion block. The processorincludes processing capabilities as well as an input/output (I/O) interface through which the processormay receive various input signals and generate a plurality of output signals (e.g., power output(s) via block). The memoryis provided for storage of data as well as instructions or code (i.e., software) for the processor. The memorymay include various forms of non-transitory memory and may include non-volatile memory for storing and accessing computer-readable instructions executable by processoras well as volatile memory (e.g., such as RAM) for storing and accessing dynamically generated data. The AC/DC power conversion block, as general functionality, is shown in simplified form and may comprise systems, topologies, and/or methods in the art.

38 46 48 50 46 1 8 The power modulealso includes a power module identification (ID) blockand operating logicthat is coupled to a synchronization logic blockfor implementing the synchronization methods described herein. The power module IDmay take various forms depending on the implementation, but functionally is used at least for purposes of identifying the particular power module in a synchronization block, which will be described below. The identification PM-PMwill be used herein for description purposes of the embodiments and the examples.

48 38 42 40 48 The operating logicof each power moduleincludes programmed logic stored in memorywhich when executed by processorperforms a number of functions, including control of charging start and stop times, management and/or reporting of faults and the like, as well as generally conforming its charging output in accordance with a charging profile requested by the vehicle. It should be understood that this description is not exhaustive of the functionality of the operating logic.

50 42 40 51 The synchronization logicin accordance with an implementation includes programmed logic stored in memorywhich when executed by the processorperforms a number of functions described herein, including the generation and transmission of a synchronization signalas well as receiving and interpretation of corresponding synchronization signal(s) received from other power modules assigned to a particular vehicle charging plug (i.e., within the same synchronization block).

51 28 51 50 a The synchronization signalis transmitted/received to/from the bidirectional bus. In an implementation, the synchronization control of the power module output(s) is decentralized in that each power module can regulate the timing or phase of its own electrical current/voltage output relative to the output(s) of other power modules in the synchronization block, in accordance with the received synchronization signal(s). The synchronization logicperforms various functions including establishing the synchronization block, determining the identity of the primary and second power modules within a synchronization block, determining its own output timing or phase, determining the output timing/phase of the other power modules in the synchronization block, as well as regulating its own output signal. In an implementation, the synchronization signal may comprise two parts. One part corresponds to digital messages in accordance with a communication protocol that allows the power modules to communicate and ultimately manage the different modules activated for a specific charging session, specify the roles each power module performs (e.g., primary power module, secondary power module(s), etc.) for a specific charging session, and the like. Another part comprises, in an implementation, a pure 50% square wave, synchronized with the working frequency of the power module (e.g., 50 Khz) that will be the heartbeat of the synchronization procedure.

51 51 51 The synchronization signalcan be isolated or not isolated depending on the architecture of the charging system. In an implementation, the power modules will be made by different parts that could be galvanically isolated from each other. In general the synchronization signals will be isolated. The synchronization signalcan also be distributed in different ways but in an implementation, two power modules (or a multiple of two) may be included in a synchronization block and the synchronization signalis communicated between the power modules in that block.

In an implementation, one of the power modules in the synchronization block is considered to be the master or primary power module and the remainder of the power modules in the synchronization block are considered secondary power module(s). The primary power module generates an output signal with an AC component (ripple) that has a baseline phase characteristic while the secondary power module(s) generate output signals also with AC components (ripple) that have respective offset phase characteristics. The number of power modules contained in a synchronized block may be an odd number as well as an even number, wherein a phase shift is equal to:

where n is the number of power modules in the synchronization block.

3 5 FIGS.- 3 FIG. 3 FIG. 2 FIG. 28 52 52 52 1 3 5 2 4 6 2 4 6 50 46 46 a a b c are block diagrams depicting various synchronization blocks of power modules, in an implementation. As described above, the power modules are connected to communication bus. The primary (main or master) power module in a synchronization block can be dynamically defined, in an implementation. For example, as shown in, in a charging system with six total power modules and three charging plugs equally loaded, there are three defined synchronization blocks,, and, with power modules PM, PM, and PMbeing the respective primary (main) power modules and power modules PM, PM, and PMbeing the respective secondary power modules. Alternatively, power modules PM, PM, and PMcould be the primary (main) power modules in the example of. Thus, the synchronization logicmay provide that the lowest module ID(see) in a synchronization block becomes the primary power module or alternatively that the highest module IDin a synchronization block becomes the primary power module. More generally, any module in the synchronization block can be the primary module as it can be a matter of assignment. The foregoing selection of the primary module is an example of role assignment.

4 FIG. 54 54 1 4 2 3 5 6 a b Similarly, as shown in, in a charging system with six power modules and two charging plugs equally loaded, two synchronization blocksandare defined, with power modules PMand PMbeing the respective primary (main) power modules and power modules PM/PMand PM/PMbeing respective secondary power modules.

5 FIG. 56 56 1 5 2 3 4 1 6 7 8 5 a b As shown in, in a charging system with eight power modules and four plugs, but only two of the plugs being equally used, there will be two synchronization blocksanddefined wherein power modules PMand PMare the primary (main) power modules with power modules PM/PM/PMbeing secondary power modules in the block with PMand power modules PM/PM/PMbeing the secondary power modules in the block with PM.

5 FIG. 1 8 In the same charging system as shown in, if one charging plug will be used, the primary (main) power modules can be any one of the eight power modules PM-PM.

3 5 FIGS.- 3 FIG. 10 thus illustrate a method of establishing a synchronization block and the primary (master) module therefor, which includes the step of determining a first number of charging plugs that have been connected to a respective BEV and that will be used. Next, determining a second number (total number) of available power modules included in the charging system. Finally, determining a third number n of power modules to include in a synchronization block, which is based on at least the first number and the second number. For example, in, the first number of charging plugs to be used is three, the second number of power modules is six, and thus the number of power modules to include in a sync block is two (i.e., six power modules divided by three charging plugs).

3 5 FIGS.- also illustrate how the master synchronization power module can be defined dynamically to establish blocks of synchronized power modules, with each synchronization block corresponding to a charging plug that is to be used. It should be appreciated that it is possible to activate, for charging purposes, less than all of the power modules in a synchronization block of power modules. For example, activating as few as just two power modules would still provide the benefit of ripple minimization.

6 FIG. 6 FIG. 6 FIG. 58 60 62 64 58 64 68 O1 O2 O3 O4 OUT SW SW depicts traces corresponding to the respectively phase-shifted output currents generated by four power modules, shown on a common timeline. Traces(I),(I),(I), and(I) show the respective AC components of the output electrical current of four power modules synchronized in a synchronization block. The period of the AC components is indicated as T. As also shown, each individual power module will have a ripple magnitude 66. One of the power modules will be considered the primary (main) power modules and will have an output with an AC component having a baseline phase characteristic. The remaining power modules in the synchronization group will be considered secondary power modules and will have an output with a respective AC component each having a respective offset phase characteristic that increases progressively. The phase shift will be as set forth above, and since the number of power modules n is four, the phase offset will be T/4, as also shown in. The summation of the four output signals-is shown as the output current trace(I), which has a reduced ripple magnitude 70 that is less than the ripple magnitude 66 of any individual power module output. It should be understood that from, the four traces are being generated from four synchronized power modules, with one of the power modules performing the role of the primary module having a baseline or reference phase, with the other three synchronized power modules performing the role of secondary modules and exhibiting a progressively larger phase offset relative to the baseline (e.g., the baseline module=0°; the next module is 90° phase offset; the next module is 180° phase offset; the next module is phase offset) 270°. In ideal circumstances, the resulting AC component (ripple current) would be zero.

In one implementation, the primary power module commands the secondary power modules their respective phase offset values to use in generating respective output signals. In another implementation, each power module is configured to calculate its own phase offset based on information pertaining to its role (primary or secondary) and position in the synchronization block.

7 FIG. 72 is a flowchart showing a method of an aspect of operating a stationary vehicle battery charging system having a first plurality of power modules and a second plurality of charging plugs. The method begins at step.

72 10 72 74 In step, the charging system(or portions thereof) establishes at least one synchronization block, each block comprising two or more of the power modules, for the purposes of charging through one of the charging plugs that is connected to a battery electric vehicle (BEV). The stepmay be performed as described above. The method proceeds to step.

74 74 76 In step, the method involves communicating at least one synchronization signal among the synchronization block power modules to synchronize respective output signals for reducing charging ripple. The stepmay be performed as described above. The method proceeds to step.

76 76 In step, the method involves charging the BEV using the synchronization block power modules. The stepmay be performed as described above.

10 It should be understood that the above steps may be performed in various ways as described herein. The charging system(or portions thereof) may configure a first power module in the synchronization block—the primary power module—to generate a first output signal having a first direct current (DC) component and a first alternating current (AC) component having a baseline phase characteristic. The first AC component has a first ripple magnitude.

10 The charging system(or portions thereof) may configure a second (or multiple secondary) power module(s) in the same synchronization block to generate a (or multiple) second output signal(s) having second DC component(s) and second AC component(s) having respective offset phase characteristic(s) that are determined such that the sum of the first AC component and the second AC component(s) results in a combined charging ripple magnitude (i.e., output being delivered to a single charging plug) that is less than the first ripple magnitude (i.e., of a single power module alone). For example only, in an implementation, if three power modules are assigned to a charging plug and thus constitute a synchronization block, the three power modules can send—over the bus—the timing and phase information regarding the electrical current the power modules supply through the plug. Each of the other power modules can receive the timing/phase information of the other power modules via the bus and shift the phase/timing based on the power output of the other two power modules. The timing and phase of the three power modules can be set so that the summed current is reduced, and within a current ripple threshold, in an embodiment, without the use of a passive L-C circuit.

10 26 10 Further, the charging system(or portions thereof) may connect (e.g., via the switch matrix) the first (primary) and second (or multiple secondary) power modules in the synchronization block to the charging plug connected to a BEV. The charging system(or portions thereof) may further control the first (primary) and second (or multiple secondary) power modules in the synchronization block to generate the first and second (or multiple secondary) output signals. As a result, in an implementation, an output ripple current is reduced, by virtue of phase shifting outputs, especially where multiple power modules are used concurrently for charging through a single plug-which obviates the need for external/expensive L-C filter(s). The modulation strategy described herein thus reduces system cost as well as improves efficiency, in implementations.

It should be understood that an electronic processor as described herein may include conventional processing apparatus known in the art, capable of executing pre-programmed instructions stored in an associated memory, performing in accordance with the functionality described herein. To the extent that the methods described herein are embodied in software, the resulting software can be stored in an associated memory and can also constitute the means for performing such methods.

It should be further understood that an article of manufacture in accordance with this disclosure includes a computer-readable storage medium (non-transitory) having a computer program encoded thereon for implementing the logic described herein. The computer program includes code to perform one or more of the methods and steps thereof disclosed herein. Such embodiments may be configured to execute on one or more processors, multiple processors that are integrated into a single system or are distributed.

It is to be understood that the foregoing is a description of one or more embodiments of the invention. The invention is not limited to the particular embodiment(s) disclosed herein, but rather is defined solely by the claims below. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to come within the scope of the appended claims.

As used in this specification and claims, the terms “e.g.,” “for example,” “for instance,” “such as,” and “like,” and the verbs “comprising,” “having,” “including,” and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.